Patent GB-361546-A (GB)
Title: Improvements in or relating to telegraphic exchange systems
IPC: H04L25/22
Filed: 1930-10-22
Abstract: 361,546. Telegraph exchange systems. LORENZ AKT.-GES., C., 1, Lorenzweg, Tempelhof, Berlin. Oct. 22, 1930, No. 31779. Convention date, Oct. 23, 1929. [Class 40 (iii).] In a telegraph installation having a normally closed circuit and central battery operation, the feeding battery at an exchange is disconnected by a change-over switch when the exchange is connected to a further exchange. The feeding battery at either the first or second exchange may be disconnected. The closed circuit in Fig. 1, which shows the exchange VM connected to a subscriber Tn extends from battery 2 through winding II of the relay SR, key Sk, and receiving magnet EM of the subscriber's station, and the position A of the change-over switch 11. A permanently closed circuit extends from the battery 2 through winding I of the relay SR and a resistance 5 which is equal to twice that of the subscriber's loop. During the transmission of a message from the station Tn, the circuit through the winding 11 of the relay SR is broken by the key Sk and by the contact sr positive and negative potentials are sent alternately to the line VL. For the reception of a message the relay ER is energized and at its contact er effects the operation of the receiving magnet EM. To prevent the operation of the sending relay SR during the operation of the relay ER, the contact er in its operated position connects winding II in a closed circuit including a resistance 6 equal to that of the lines 3, 4 and the receiving magnet EM so that the current flowing in the winding II of the relay SR remains unaltered. To allow for the lag in the rise of the current to its steady value due to the self-induction in the lines 3, 4 when the contact er returns to its rest position, a condenser 10 is connected to the interrupting point, in series with a resistance, if necessary, with adjustment so that current flows through winding II of the relay SR until the current in the original closed circuit reaches its steady value. When the exchange VM is connected to a second exchange VM<1> (Fig. 2 being associated with Fig. 1) either the feeding battery 2 or 2<1> is disconnected from the line by a change-over switch 11 or 11<1> respectively so that the batteries are not connected in opposition. On the assumption that the battery 2 is disconnected by moving the switch 11 to the position B, the contact er during the transmission of a message to the exchange VM<1> operates the relay SR<1> and its contact sr<1> to transmit the message from the exchange VM<1> to a subscriber or to a further exchange. During the operation of the contact er the current through the winding II of the relay SR is maintained through the resistance 6 which, in this case, is equal to that of the lines 3<1>, 4<1> and of the winding II of the relay SR<1>. To allow for the time lag in the lines 3<1>, 4<1> when the contact er returns to its normal position the condenser 10, which may have a resistance in series, is connected in a closed circuit through winding II of the relay SR. Similarly when the exchange VM<1> is transmitting to VM the operation of the contact er<1> is prevented from operating the sending relay SR<1> by the inclusion of the resistance 61 and of the condenser 101 respectively. The battery 2<1> may be disconnected by moving the switch 11<1> to the position B<1>, the battery 2, in this case, being connected to the line.